This invention relates generally to clamps for use with plastic tubing and more specifically to roller clamps for regulating the fluid flow through plastic tubing.
Plastic tubing is extensively employed in parenteral solution administration sets for use in hospitals. Numerous devices such as pinch, screw and roller type clamps have been proposed to regulate the fluid flow rate of the solution reaching the patient by compressing the tubing to vary the size of the tubing lumen. A recurring problem of maintaining a constant flow rate desired for a particular patient has been encountered because of the tendency of the tubing wall to cold flow when compressed under pressure. The phenomena of cold flow produces a migration of the tubing wall causing a progressive change in the cross-sectional areas of the lumen and therefore, the fluid flow rate. Some prior art roller clamps have increased the force of compression against the tube in an attempt to control cold flow. However, this increased force of compression has aggravated the difficulties of cold flow. As a result of the necessity of maintaining an accurate fluid flow rate, frequent monitoring and readjustment of prior roller clamps is required to insure the prescribed flow rate of fluid for the particular patient.
Roller clamps have been proposed to compensate for the phenomena of cold flow by compressing the edges of the tubing against a surface having a centrally disposed channel of varying cross-section to regulate the flow rate by the channel. For example, U.S. Pat. No. 3,685,787 discloses a clamp having a roller spaced above a compression surface to squeeze the opposite edges of the tubing permitting the central portion of the tube to flow into a longitudinal channel in the compression surface to form a lumen. The configuration and cross-sectional area of the channel in that clamp permitted cold flow migration of the compressed tubing wall into the excess channel space causing fluctuations in the desired flow rate. U.S. Pat. Nos. 4,013,263 and 4,047,694 disclose improvements to the embodiment of the U.S. Pat. No. 3,685,787 to direct the cold flow away from the excess space in the channel by providing a series of ridges along the channel to increase the compression on the tubing in an attempt to block cold flow migration into the channel and a recessed roller to permit migration into this additional space. To a certain extent, these improvements tended to direct the cold flow migration of the tubing wall away from the excess space in the channel, but permitted the formation of secondary lumens at the opposite sides of the tubing. As the tubing wall begins to relax causing the cold flow migration, the secondary lumens change size with a corresponding fluctuation in fluid flow rate.
Roller clamps require that the operator apply a manual force to longitudinally move the roller to the desired flow rate setting, both initially and during readjustment of the flow rate to compensate for fluctuations attributable to the phenomena of cold flow. With prior roller clamps, the thumb pressure applied during the manipulation of the roller added to the compressive force on the tubing making it difficult for the operator to effectively adjust the rate setting of those clamps. Specifically, after the operator set the clamp for a desired flow rate by applying thumb pressure to longitudinally position the roller, the flow rate had a tendency to immediately increase slightly. The elimination of the thumb pressure and the corresponding reduction in the compression force of the roller against the tubing caused the size of the lumen to increase producing an undesirable increased fluid flow rate.
Generally, prior roller clamps have been designed to be inexpensive to manufacture of low cost plastic materials in large quantities and are usually disposable. However, it has been difficult to adequately insure manufacturing tolerances within acceptable limits and still maintain low manufacturing costs for prior roller clamp designs. Consequently, problems such as flow rate fluctuations due to cold flow and inability to completely shut off fluid flow were encountered during the use of prior roller clamp designs as a result of the difficulties in monitoring quality control during manufacturing.